Additional loop-gap resonators were constructed to operate at various frequencies from 2-4 GHz. The project involved calculating resonant frequencies, testing resonators, and implementing them into ESE experiments in the S-band user facility. These resonators, with improved coupling loops, extend the frequency selection and improved the sensitivity greatly in our pulsed S-band EPR facility. Open-end resonators also have been designed and built to operate at L-band (1-2 GHz) for the study of biological samples. New open designs for in vivo EPR are being developed. A novel resonator/coupler holder that permits more accurate adjustment of coupling and rapid resonator exchange was constructed. This is a continuing, multi-year project.